European Oak Bark Beetle Screening Aid Scolytus intricatus (Ratzeburg) Joseph Benzel 1) Identification Technology Program (ITP) / Colorado State University, USDA-APHIS-PPQ-Science & Technology (S&T), 2301 Research Boulevard, Suite 108, Fort Collins, Colorado 80526 U.S.A. (Email: [email protected]) This CAPS (Cooperative Agricultural Pest Survey) screening aid produced for and distributed by: Version 5 USDA-APHIS-PPQ National Identification Services (NIS) 30 June 2015 This and other identification resources are available at: http://caps.ceris.purdue.edu/taxonomic_services The European oak bark beetle, Scolytus intricatus (Ratzeberg) (Fig. 1), is a widely distributed pest in Europe. This species primary host is oak (Quercus) but they will also infest other hardwood tree species including chestnut (Castanea) and hazelnut (Corylus). The adults and larvae feed in the cambium of tree branches and in the trunk, damaging the tree by girdling it and spreading pathogenic fungi (Figs. 2-3). Scolytus intricatus is a member of the Curculionidae (subfamily Fig. 1: Scolytus intricatus in tree Scolytinae) which is comprised of weevils and bark beetles. Members of (photo by, Milos Knizek, Forestry this family are highly variable but almost all species share a distinct club and Game Management Research on the end of their antennae consisting of three segments. The subfamily Institute, Bugwood.org). Scolytinae, to which Scolytus belongs, consists of the bark beetles. In general, members of Scolytinae are small (<10mm long) pill shaped beetles of a reddish brown, black, or tan color. Some authors consider Scolytinae to be a distinct family (Scolytidae). The genus Scolytus contains over 100 species, 25 of which are native to North America. It is the only genus in Scolytini to occur in temperate climates. The genus has a wide distribution, inhabiting all of Eurasia and the Americas. It can be distinguished by a steeply acending second abdominal ventrite which. in some species, is embellished by one or more large tubercles, and by protibia unarmed except for a single large lateral spur which extends from the outer apical angle. Scolytus intricatus has not yet been detected in the United States. However two other species within the gunus, S. multistriatus and S. schevyrewi (Figs. 4-5) have established themselves here and are known vectors for dutch elm disease. A quality, high powered microscope is required to examine the characters necessary to identify these beetles. This aid is designed to assist in the sorting and screening of S. intricatus suspect adults collected through visual survey in the continental United Fig. 2: Scolytus intricatus galleries States. It covers basic Sorting of traps, First Level, and Second Level (photo by Gyorgy Csoka, Hungary screening, all based on morphological characters. Basic knowledge of Forest Research Institute, Bugwood. Coleoptera morphology is necessary to screen for S. intricatus suspects. org). Coleoptera 1 Scolytinae European Oak Bark Beetle Sorting Scolytus intricatus (Ratzeburg) Insects collected during Scolytus intricatus surveys should be sorted initially for the presence of beetles of the appropriate size color and shape. 1. Beetles are between 2 mm (0.1 inches) and 3 mm (0.15 inches) in length. 2. Beetles are pill-like in shape. 3. Beetles are black, reddish-brown, or tan colored. Beetles meeting these requirements should be forwarded to Level 1 Screening (Page 3). Figs. 4 and 5: The smaller European elm bark beetle: Scolytus multistriatus (top), and the banded elm bark beetle: Scolytus schevyrewi (bottom). These two European species feed on elm trees and are well established in the United States. Both species have impacted native and exotic elm trees in the U.S. (photos Fig. 3: Tree attacked by Scolytus intricatus. During a bark by Joseph O’Brien, USDA Forest Service (top) and beetle attack trees will show little sign of damage other than Whitney Cranshaw, Colorado State University (bottom), a series of small bore holes. Often it is not apparent that bark Bugwood.org). beetles have infested a tree until after they have emerged from it (photo by Jan Liska, Forestry and Game Management Research Institute, Bugwood.org). Coleoptera 2 Scolytinae European Oak Bark Beetle Level 1 Screening Scolytus intricatus (Ratzeburg) Suspect adults should be pointed and properly labeled. Level 1 Screening is based on characteristics of the, antennae, general dorsal surface, protibia and abdomen. Specimens with these traits should be forwarded to Level 2 Screening. Antennae Scolytids have relatively stout, geniculate, clubbed antennae. The clubs are made up of three antennomers and can be solid, annulated, or occasionally lamellate. The scape will always be noticable if not well developed (Fig. 6). Fig. 6: Antennae of Scolytus spp. General Dorsal Surface Note the scape and large three part club. Beetles in the tribe Scolytini have the basal margins of their elytra unarmed and forming a straight line across the body (Fig. 7). The scutellum of tribe members is usually large and flat and the head is usually concealed at least partially by an enlarged pronotum. Protibia The protibia of the Scolytini tribe are distinguishable by being armed only with a large lateral spur exending from the outer apical angle (Fig. 8). Most other Scolytinae have protibia armed by several small spines along Fig. 7: Base of elytra and scutellum the lateral margin. of Scolytus spp. Members of the Scolytini tribe should have a broad Abdomen scutellum and the base of the elytra should be unarmed. In most members of the Scolytinae, including S. intricatus, the second ventrite of the abdomen steeply acends producing an oblique plain between the first and third ventrites (Figs. 9 and 10). Fig. 8: Protibia of Scolytus spp. Members of the Scolytini tribe have only a single apical spine on the protibia (circled). Figs. 9 and 10: Postrolateral (left) and lateral (right) views of Scolytus spp. abdomen. In this genus the second ventrite is raised at an oblique angle so that the abdomen meets the only slightly declivous elytra. The ventrites may be armed with one ore more spines or tubercles of varying size depending on the species. Coleoptera 3 Scolytinae European Oak Bark Beetle Level 2 Screening Scolytus intricatus (Ratzeburg) Fig. 11-13: Dorsal view of non-native Scolytus species. No native Scolytus feed on hardwoods as do Palearctic species. However, both S. schevyrewi (middle) and S. multistriatus (right) have become established in the U.S. These two species infest elms so their presence in oaks would be atypical. Fig. 11: Scolytus intricatus (target) Fig. 12: Scolytus schevyrewi Fig. 13: Scolytus multistriatus Level 2 screening is designed to screen out potential S. intricatus (Fig. 11) from other members of Scolytini. In general, surveys for S. intricatus should detect only a few other members of the tribe. In the Scolytini, only the genus Scolytus occurs in the Temperate regions and most native species feed exclusively on conifers. In addition to S. intricatus, other nonnative species which have become well-etablished in North America, such as S. schevyrewi and S. multistriatus (Figs. 12-13), may be found during surveys. Screening is based on general dorsal surface, the abdomin, and the frons. General Dorsal Surface Scolytus intricatus is a relativly small bark beetle ranging in length from 2-3 mm (0.1-0.15 inches). The body color is black with reddish brown elytra and light brown antennae and legs (Fig. 11). This coloration is readily distinguishable from that of S. schevyrewi which is lighter in color and often possesses a distinct black or dark brown band across its elytra (Fig. 12). Abdomen The abdominal ventrites of S. intricatus members are not armed with any form of spine or tubercle (Fig. 14) as would be seen in many Scolytus species such as S. quadrispinosus and S. unispinosus (Figs. 15-18). Some other native Scolytus lack tubercles as well (Figs: 19-21). Frons The frons is distinctive only in male Scolytus which can be distinguished by having this area of the body flattened and with a series of impressions. Scolytus intricatus males have a flattened frons armed with two brushlike patches of dense pubesence (Fig. 22). In most native scolytus the frons usually bears a shallow or marked impression and the patches of pubesence are not present (Fig. 23). Coleoptera 4 Scolytinae European Oak Bark Beetle Level 2 Non-targets Scolytus intricatus (Ratzeburg) Fig. 14: Scolytus intricatus (target). Fig. 15: Scolytus schevyrewi. Fig. 16: Scolytus multistriatus Fig. 17: Scolytus quadrispinosus Fig. 18: Scolytus unispinosus Fig. 19: Scolytus ventralis Figs. 14-21: Scolytus abdomens in postrolateral view. note the lack of spines on the progressively rising ventrites of the S. intricatus abdomen (top left). Fig. 22-23: Frons of male S. intricatus (left) and S. ventralis (right). In S. intricatus, the frons is flattened and the bottom margin has two patchs of closely clumped setae (circled). Native Fig. 20: Scolytus rugulosus Fig. 21: Scolytus reflexus Scolytus bear at least a shallow depression and no setae patches. Suspect S. intricatus specimens, (those with unbanded elytra, a raised second ventrite but otherwise unarmed abdomen, and if male, a flatted frons bearing two dense patches of setae) should be sent forward for identification. Specimens must be labeled and carefully packed to avoid damage during shipping. Fig. 22: Scolytus intricatus (target). Fig. 23: Scolytus ventralis Coleoptera 5 Scolytinae European Oak Bark Beetle Key and References Scolytus intricatus (Ratzeburg) Key to Sort and Screen Scolytus intricatus Suspects in the United States 1. Beetles approxmately 2-3 mm long; pill shaped and with black; brown, or tan coloration............... 2 1’. Beetles larger or smaller than 2-3 mm long; not pill shaped; or color not a shade of black, brown, or tan .............................................................................................................Not S. intricatus 2. Antennae geniculate with a large club made up of three segments on the end (Fig. 6); basal margins of elytra unarmed and forming a straight transverse line accross the body (Fig.